1. Field of the Invention
The invention is directed to methods of promoting osteogenesis by administering a p38 MAP kinase inhibitor. More specifically, the invention is directed to methods of treating bone fractures, bone diseases, bone grafting, especially enhancing bone healing following facial reconstruction, maxillary reconstruction, mandibular reconstruction or tooth extraction, enhancing long bone extension, enhancing prosthetic ingrowth, and increasing bone synostosis by administering a p38 MAP kinase inhibitor.
2. Background
Bone is subject to constant breakdown and resynthesis in a complex process mediated by osteoblasts, which produce new bone, and osteoclasts, which destroy bone. Osteoblasts secrete osteoid, the unmineralized organic matrix that subsequently undergoes mineralization which provides strength and rigidity to bone.
One condition in which enhanced bone formation is required is bone fracture. After a bone fracture, it is desirable to stimulate bone growth so as to hasten and complete bone repair. There are approximately six million bone fractures in the United States each year. The complication rate associated with fracture healing has been estimated at 5-10%. Complications such as non-union, delayed union, and mal-union can occur. The etiology of the complications remains unknown but certain factors are known to negatively affect the outcome of fracture healing. These effects include age, diabetes, and NSAID (non-steroidal anti-inflammatory drug) use.
Fracture healing is a complex process. Preferably the fracture healing process restores a broken bone to its prior metabolic and mechanical functional state. The initial events that occur following a fracture include tissue hypoxia and hematoma formation. The tissue hypoxia and hematoma formation quickly lead to inflammation and edema in the soft tissues surrounding the fracture site. Cell proliferation soon begins to occur rapidly in the periosteum (the osteoblast cell layer around the bone) within the vicinity of the fracture site called the fracture callus. Mesenchymal cell migration falls rapidly during the inflammation phase and it is thought that the fibrin clot formed from the hematoma acts as a source for cell attachment at the fracture site for the migrating cells. The source of the migrating mesenchymal cells remains controversial but probably includes circulating mesenchymal stem cells mobilized from the bone marrow, vascular pericytes, and proliferating muscle satellite cells. The cells that have migrated into the fracture site differentiate into chondrocytes and form a cartilaginous matrix. Endochondral ossification progressively proceeds from the junction between the osteoblasts that have proliferated from the periosteum and the differentiated chondrocytes within the fracture site so that new bone formed from endochondral ossification fills the fracture callus from the periphery to the actual fracture site. Chondrocytes at the osteoblast-chondrocyte boundary terminal differentiate into hypertrophic chondrocytes, express Type X collagen, secrete angiogenic factors, and mineralize the cartilaginous matrix (calcified cartilage). Osteoblasts at the osteoblast-chondrocyte junction secrete new bone. As angiogenesis occurs at this boundary, osteoclasts migrate into the area, resorb the calcified cartilage, which is then replaced with new bone secreted from the osteoblasts. Ultimately, this process bridges the fracture site and the bone is remodeled based upon the mechanical stresses imposed upon the bone.
Protein kinases are involved in various cellular responses to extracellular signals. p38 Mitogen-Activated Protein (MAP) kinase (also called p38 kinase or “High Osmolarity Glycerol response kinase” (HOG)) is a member of a family of signaling molecules known as the Mitogen-Activated Protein kinase (MAP kinase or MAPK) family. Other members of the MAP kinase family include the classical MAPKs termed Extracellular signal Regulated Kinases (ERK), which are activated by a variety of mitogenic stimuli as well as differentiation signals, and Stress-Activated Protein Kinases (SAPK) (also called Jun N-terminal Kinases (JNK)). SAPKs are activated by stresses but not mitogens, like the p38 MAP kinase.
p38 MAP kinase is activated by a variety of cellular stressors, including ultraviolet radiation, osmotic shock, and inflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α). Once activated, p38 MAP kinase mediates the induction of mRNA synthesis for a variety of inflammatory mediators, including IL-1β, TNF-α, IL-6, and cyclo-oxygenase-2 (COX-2).
Four isoforms of p38 MAP kinase have been identified and are designated as p38α, p38γ, p38δ and p38δ (Jiang, Y. et al., J. Biol. Chem. 271:17920-17926 (1996); Kumar, S. et al., Biochem. Biophys. Res. Comm. 235:533-538 (1997); Stein, B. et al., J. Biol. Chem. 272:19509-19517 (1997); Li, Z. et al., Biochem. Biophys. Res. Comm. 228:334-340 (1996); Wang, X. et al., J. Biol. Chem. 272:23668-23674 (1997)). p38α is also referred to as p38. p38β is also referred to as p38-2. p38γ is also referred to as ERK6. These isoforms differ in tissue expression patterns, substrate utilization, response to direct and indirect stimuli, and susceptibility to kinase inhibitors. For example, one study has demonstrated the activation of p38β MAP kinase results in myocyte hypertrophy, while the activation of p38α MAP kinase leads to myocyte apoptosis (Wang, Y. et al., J. Biol. Chem. 273:2161-2168 (1998)).
Inhibition of p38 MAP kinase leads to a blockade on the production of both IL-1 and TNF. IL-1 and TNF stimulate the production of other proinflammatory cytokines such as IL-6 and IL-8 and have been implicated in acute and chronic inflammatory diseases and in postmenopausal osteoporosis (Kimble, R. B. et al., Endocrinol. 136:3054-3061 (1995)). Based upon this finding it is believed that p38 MAP kinase, along with other MAPKs, have a role in mediating cellular response to inflammatory stimuli, such as leukocyte accumulation, macrophage/monocyte activation, tissue resorption, fever, acute phase responses and neutrophilia. In addition, MAPKs, such as p38 MAP kinase, have been implicated in cancer, thrombin-induced platelet aggregation, immunodeficiency disorders, autoimmune diseases, cell death, allergies, osteoporosis and neurodegenerative disorders. Other diseases associated with IL-1, IL-6, IL-8 or TNF overproduction are set forth in WO 96/21654.